Introduction

The growing global water crisis threatens the security, stability and environmental sustainability of developing nations. Millions die each year from water-borne diseases, while water pollution and ecosystem destruction grow, particularly in the developing world. In its recent Millennium Declaration, the UN called on the nations of the world "to halve by the year 2015 (...) the proportion of people who are unable to reach, or to afford, safe drinking water" and "to stop the unsustainable exploitation of water resources, by developing water management strategies at the regional, national and local levels, which promote both equitable access and adequate supply".

Over the past few decades there has been an increasing acceptance that the management of water resources must be undertaken with an integrated approach, that assessment of the resource is of fundamental importance as the basis for rational decision-making and that national capacities to undertake necessary assessments must be fully supported. Management decisions to alleviate poverty, to allow economic development, to ensure food security and the health of human populations as well as preserve vital ecosystems, must be based on our best possible understanding of all relevant systems.

The World Water Assessment Programme (WWAP) focuses on assessing the developing situation as regards freshwater throughout the world. The primary output of the WWAP is the periodic World Water Development Report (WWDR). The Programme will identify situations of water crisis and will thus provide guidance for donor agencies and will provide the knowledge and understanding necessary as the basis for further capacity building.

The Programme, including the new WWDR, is undertaken by the UN agencies concerned aided by a Trust Fund, donors providing support in cash and in kind either through specific agencies or through the Trust Fund. UNESCO currently hosts the WWAP Secretariat and manages the FUND at its Headquarters in Paris.

In the framework of WWAP the Center for Environmental Systems Research was asked to prepare global maps illustrating the current state of the world freshwater resources.

Objectives

The specific objectives of the project are to carry out global analyses needed to provide water managers and other stakeholders with the latest information about the current state of the worlds freshwater resources. The global analyses focus especially on the assessment or current state of both water availabilities and water withdrawals. Water withdrawals are split up into different sectors to estimate the fractions of total withdrawals the single sector claim for. Furthermore analyses were carried out to assess water stress on country and catchment level.

Study approach

This project involves several practical steps. First, the information to be provided was discussed with the Secretariat of the World Water Assessment Programme. The next step involves the preparation of the necessary inputs for the global analyses, which are performed using the WaterGAP model model. This model allows the conversion of assumptions about socio-economic and climate trends into trends of water withdrawals and water availability. Third, the WaterGAP model model is run using the prepared inputs, and model results are evaluated. The last step includes the presentation of results in different forms, according to the necessities of the WWAP.

WaterGAP 2.1

Model description (130KB, pdf)

Examples for model applications

• Critical regions: A model-based estimation of world water resources sensitive to global changes (500KB, pdf)
• Global estimates of water withdrawals and availability under current and future “business-as-usual” conditions (890KB, pdf)